Organic electroluminescent devices include an organic layer (hereinafter sometimes referred to as a “light-emitting unit”) provided by placing organic charge transport layer(s) and organic light-emitting layers between an anode and a cathode. Electroluminescent devices often can provide high-intensity light emission while being driven by direct current and low-voltage. Electroluminescent devices have all constituent elements formed of a solid material and have the potential for being used as flexible displays.
The performance of some electroluminescent devices can deteriorate over time. For example, light emission characteristics such as light emission intensity, light emission efficiency and light emission uniformity can decrease over time. The deterioration of the light emission characteristics can be caused by oxidation of the electrode due to oxygen permeating into the organic electroluminescent device, oxidative decomposition of the organic material due to generation of heat from driving the device, corrosion of the electrode due to moisture in the air that permeates into the organic electroluminescent device, or breakdown of the organic material. Furthermore, interfacial separation of the structure may also give rise to deterioration of the light emission characteristics. The interfacial separation can result, for example, from the effects of oxygen or moisture and from the effects of heat generation while driving the device. Heat can trigger interfacial separation due to the generation of stress resulting from differences in the thermal expansion coefficients between adjacent layers.
Organic electroluminescent devices are sometimes encapsulated with a polymeric material so as to protect the device from contact with moisture and/or oxygen. However, many polymeric materials are insufficient because of their hermetic sealing properties, moisture resistance, moisture barrier properties, and the like. If a thermally curable polymeric material is used, heat is used to cure the material, which can result in deterioration of the organic light-emitting layer and/or charge transfer layer, or the light-emitting characteristics of the device can deteriorate due to crystallization. If a photocurable polymeric material is used, UV radiation is often used to cure the material, which can result in deterioration of the organic light-emitting layer and/or charge transfer layer. After the polymer material is cured, it can crack due to impact, bending, or vibrations which may occur when the device is used, and which can also lead to deterioration of the performance characteristics of the device.